General microbiology - viruses, bacteria, fungi >>>> Cross-resistance

Cross-resistance.

Antibiotic cross-resistance.

The basis of the immunity of microorganisms to antimicrobial drugs is natural or acquired resistance. As noted here, microorganisms (in particular, bacteria) have a variety of anti-drug capabilities. In fact, the presence of natural resistance in bacteria to certain antibiotic actions exerted on the target makes it invulnerable and leads to the ineffectiveness of antibacterial therapy.

But of special interest for medical science is the fact that microorganisms can be resistant to antibacterial drugs that have never interacted with before. Research carried out in this area made it possible to collect and systematize data on some types of bacteria (staphylococcus, shigella, escherichia, proteus, Moraxella, Citrobacter, Acinetobacte, Providenciae), which are resistant not only to drugs of the same group and several generations with the same pharmacodynamics, but and to antibacterial drugs of other groups.

Modern methods circumvent antibiotic resistance bacteria constructed to change the group of antibacterial agents, and these techniques are effective, but only under the condition that the bacteria do not have the stability and the new selected drug (with respect to such preparations bacteria have «cross-resistance»). Based on the facts revealed in the process of studying this side of the issue, the following mechanisms of natural cross-resistance of bacteria to some groups of antibiotics can be distinguished.

For example, antibiotic cross-resistance of bacteria inhibiting the action of enzymes synthesized by bacteria (cephalosporinases, penicillinases, carbapenemases and other beta-lactamases, penicillin-binding proteins), creates situations when drugs of the group of synthetic penicillins and cephalosporins against certain strains (for example, staphylococcus, and such strains) will be ineffective drugs are said to exhibit cross-resistance. In such cases, combinations of systemic antibiotics with inhibitors of the aforementioned enzymes (amoxicillin and clavulanic acid, ampicillin and sulbactam, etc.) are prescribed, where clavulanic acid, sulbactam, tazobactam act as an inhibitor, or give preference to combined antibiotics, which include two components at the same time.

Bacteria exhibit a similar cross-resistance to aminoglycosides (by synthesizing aminoglycoside-modifying enzymes), to fluoroquinols (by modifying bacterial enzymes: DNA gyrase and topoisomerase IV), to macrolide, lincosamide and streptogramin antibiotics (by modifying ribosomal enzymes) to tetracyclines (by modifying the ribosome and / or active elimination), to glycopeptides and sulfonamides (by modifying the target) and other groups of antibacterial drugs.

Cross-resistance in insects.

It should be noted that cross-resistance is not only a property of microorganisms (bacteria, viruses, fungi, etc.), it is also observed in insects.

It was noticed that the systematic treatment of 15-20 generations of ticks with the same insecticide leads to the development in insects of this type of resistance not only to the selected insecticide or pesticides of this class, but also to pesticides of other classes.

Cross-resistance of insects to pesticides is developed due to the fact that they can produce enzymes in the body that oxidize and remove harmful metabolites from the body. Thus, insects that have developed resistance to organophosphate insecticides show cross-resistance to organochlorine insecticides. And resistance to pesticides, derivatives of carbamic acid, determines the resistance of insects to organophosphorus compounds. Therefore, it is customary to alternate insecticides not of the same class, but of different chemical classes, taking into account the possible cross-resistance to chemical compounds.